The objectives of this proposal are to isolate and characterize a comprehensive series of deletion mutants of human adenovirus types 2 and 5, and to use them to probe the processes of transformation by adenovirus and regulation of adenovirus gene expression. Deletion mutants obtained from stocks containing naturally arising defective adenovirus variants and those constructed enzymatically using restriction endonucleases will be cloned using a complementation plaquing technique. Their deletions will be mapped using electron microscopic examination of heteroduplex DNA molecules, and the mutants will be characterized biochemically. Mutants unable to transform cells and mutants with regulatory abnormalities will be examined in detail, and the viral functions important in transformation and regulation will be defined.